I will install macOS Sierra
What should I do before formate ?
How I can reinstall the f-secure freedome again?
There is nothing to be done before the reformat. After the reformat, you can install Freedome on your Mac and refer to this article for the installation instructions.
In case you have used up all your licenses in the multi device subscription, Freedome will prompt for a license transfer during the installation. This article explains the license transfer feature. Please have a look.